Electronic tremulant



OC- 2, 1962 H. o. SCHWARTZ ETAL 3,056,327

ELECTRONIC TREMULANT Filed June 9, 1960 United States Patent Office 3,056,327 Patented Oct. 2, 1962 3,056,327 ELECTRONIC TREMULANT Harold O. Schwartz and Carl L. Wolgast, North Tonawanda, N.Y., assignors to The Wurlitzer Company, Chicago, Ill., a corporation of Ohio Filed June 9, 1960, Ser. No. 34,919 Claims. (Cl. 84-L25) The present invention relates to electronic musical instruments in which electronic tone signals are amplified and transformed into audible sounds, and is concerned more particularly with the achievement of tremulant effects in the audio output of such instruments.

One object of the invention is to provide, in an electronic musical instrument, such for example as an electric organ, new and improved means for generating sound with tremulant effects from electronic tone signals.

Another object is to provide, in an electronic musical instrument, new and improved electronic tremolo means which operate electronically to introduce tremulant effects into the generation of sound from electronic tone signals.

Another object is to provide new and improved sound generating means having a wholly electronic mode of operation, which generates sound with pleasing tremulant effects from separately supplied `electronic tone signals and cyclic electronic signals.

A further object is to provide, in an electronic musical instrument, new and improved tremolo means which respond to simple electronic cycle signals emciently to introduce a highly effective tremulant character to electronic tone signals, which then generate sound with tremulant effects.

Another object is to provide new and improved electronic sound generating means in which pleasing tremolo effects are achieved by the reflection of the variable resistance of a vacuum tube into an electronic sound channel of the sound generating means.

A further object is to provide in an electronic musical instrument, new and improved tremolo means which is more compact, less expensive, and more stable and dependable in operation than prior tremolo devices used for the same purpose.

Other objects and advantages will become apparent from the following description of the exemplary embodiments of the invention illustrated in the drawings, in which:

FIGURE l is a diagrammatic illustration of an electric organ incorporating one embodiment of the invention; and

FIG. 2 is a diagrammatic illustration of an electric organ incorporating another embodiment of the invention.

Referring to the drawings in greater detail, the electronic organ 1t) illustrated in lFIG. l and forming the first illustrated embodiment of the invention, comprises a tone generator 12 which produces electronic tone signals which are amplified in an amplifier 14.

The output of the amplifier 14 is connected to a crossover network 16 which separates the high or treble frequency in the amplifier output from the low or bass frequency in the amplifier output. The high frequency output channel i8 of the crossover network 16 is connected to drive a treble speaker 20, and the low frequency output channel 22 of the crossover network 16 isy connected to drive a bass speaker 24.

Tremulant effects are generated in the low frequency output channel 22 connected to the bass speaker 24. Such tremulant effects, which are produced in a manner to be described, are achieved by a cyclic variation in the output volume of the low frequency channel. Thus, the output volume is varied at a tremulant frequency which should be of the order of 6.5 cycles per second.

To control the tremulant frequency, a suitable electronic cycling device 26 is provided for supplying to a tremolo control switch 28 an output voltage which is varied cyclically at a rate of 6.5 cycles per second. A device capable of supplying a voltage which is varied cyclically at this rate can be readily provided by those skilled in the art, and hence need not be described here in order to convey an understanding of the present invention.

Upon closure of the tremolo control switch 28, the cyclic signal voltage supplied through the switch 28 is used to produce a corresponding cyclic variation in the plate resistance of two vacuum tubes 30, 32. The variable plate resistance of the tubes 3ft, 32 is refiected into the low frequency output channel 22 of the crossover network 16, to effect a corresponding cyclic variation in the volumetric output level of this channel.

As shown, the cathodes of both tubes 30, 32 are connected to ground through a resistor 34 and a capacitor 36 in parallel. The control grids of both tubes are connected to ground through a resistor 38 and coupled through a capacitor il with the output side of the vibrato control switch 2S, whereby the alternating voltage sup plied through the switch 2S is applied to the grids of both tubes.

The plates of the respective tubes 3i), 32 are connected to two vibrato control coils 4t), 42, wound on a magnetic core 45. A D.C. voltage is supplied from a conductor 44 to the ends of the coils 40, 42 opposite from the tubes 3l), 32. The windings of the coils 4f?, 42 in the directions of current flow through the respective coils are such that the coils are in magnetically bucking relation to each other.

Referring again to the crossover network 16, it will be observed that the input terminals of the bass speaker 24 are bridged by a capacitor 48 and that one of the terminals is connected to the amplfier 14 through an inductance or high frequency choke coil 50.

The inductance coil 50 included in the power supply to the bass speaker 24 is wound on the same magnetic core 45 on which the tremolo control coils 40, 42 are wound.

The operational effect of this structure is to reflect into the bass` channel 22 which drives the speaker 24 the cyclically varied plate resistance of the tubes 30, 32.

Thus, the cyclically varied grid voltage on the tubes 30, 32 effects a corresponding variation in the current flow through the tremolo control coils 40, 42, which in turn effects a cyclic variation in the flux in the core 45. The effect of this is to produce a cyclic variation in the effective inductance of the inductance coil 50, with the result that the impedance in the circuit which drives the bass speaker 24 is varied cyclically at a lfrequency of 6.5,

cycles per second. This cyclic variation in the imped-ance of the bass speaker driving circuit causes a corresponding cyclic variation in the amplitude or output volume of the sound signals from the bass speaker to produce the desired tremulant effect in the sound generated.

Since the coils 40, 42 magnetically buck each other,

changes in the current ow through these coils at the trem-V ulant frequency of 6.5 cycles per second do not cause any corresponding induced voltage in the inductance coil 50. Moreover, transformer coupling efficiency at this low Lfrequency is extremely poor, Consequently, no problem arises from a voltage being induced in the coil 50 by `changes in the current fiow through the coils 40, 42.

Moreover, a very high turns ratio of the. coils 40, 42 relative to the Acoil 50 is used to effect an impedance match between the coils 40, 42 and the tubes 30, 32, while at the same time limiting the turns of the coil 50, so as to avoid undue attenuation of the power supply through the coil 50 tothe bass speaker 24.

The variable Iaudio voltage vapplied to the coil 5t) is -steped up in the coils 40, 42 and applied to the plates of the tubes 30, 32. Interference with the effectiveness of the tubes 30, 32 in impressing a tremulant eiiect on the bass sound, by the transformed audio voltage on the tubes 30, 32, is effectively avoided by the push-pull relationship of the tubes to the coils titi, 42, and by the application of a DC. voltage to the conductor 44 which is suiiiciently high to operate the tubes 3G, 32 at high plate currents.

yIt will be appreciated that the tremolo means thus provided operates to produce a tremulantreiiect in the low frequency sound only when the tremolo control switch 28 is closed.

A modified embodiment of the invention is incorporated into an electric organ 60, illustrated diagrammatically in FIG. 2. For simplicity in description, component elements of the ongan 6@ which `are similar to previously described components of the organ l0 are designated with the same reference numbers, with the addition of the suffix a.

Thus, `as illustrated, electronic tone signals from the tone generator 12a are arnpliiied in an amplifier l/ta and supplied to a crossover network 16a which has a high frequency output channel 18a connected to a treble amplier 62 which drives a treble speaker Zita.

The bass speaker 24a is driven -rby a bass amplilier 6d which connects with the low frequency output channel 22a of the crossover network ta through means which incorporates tremulant effects into the electronic tone signals supplied to the bass ampliiier.

As shown, the bass frequency channel 22a of the crossover network 16a comprises a high frequency choke coil 66 which is coupled to ground through a capacitor 63 and a resistor 70.

The low frequency laudio signal supplied at the output end of the choke coil 66 is connected through an inductance coil 72 to one side of the bass ampliiier 6d, the other side of which is grounded, `as shown. A lresistor 74 is connected across the input terminals of the amplifier 64. The desired tremulant efects are introduced through the coil 72 into the tone signals supplied to the input of the bass -ampliiier 64.

For this purpose, the coil 72 is wound on a magnetic core 45a corresponding to the core 44 used in the organ 10, previously described. Two tremulant control coils 40a, 42a wound on the core 45a in magnetically bucking relation to each other are cyclically energized `by electronic tremulant control structure corresponding to that used to energize the control coils `40, 42 in the organ l@ described. It will be noted with reference to FIG. Z that a potentiometer 80 is connected in series with the coupling capacitor 41a to provide for adjustment of the cyclic voltage applied to the grids ofthe tubes 30a, 32a. This provides a convenient control of the degree of tremulant eifect produced in the low `frequency sound upon closure of the switch 28a.

The amplification of the output signals of the crossover network 16a of the organ 60 permits the usage of a crossover network having a relatively high impedance. The coil 72 and the resistance 74 in the low `frequency output channel 22a of the crossover network lla serves as a resistive voltage divider which supplies a tone signal voltage to the bass amplier 64.

It will be appreciated from Athe `foregoing description that the cyclically varied plate voltage of the tubes Stia and 32a is reiiected into the coil 72 to provide the desired tremulant eifect. Because of the relatively high impedance of the crossover network 16a, which is ahead of the amplifier 64, the turns ratio of the coils 4tlg, 42a relative to the coil 72 can be substantially reduced, while at the same time providing an impedance match with the tubes 30a, 32a. This effects a corresponding reduction in the transformed audio voltage `applied to the plates of the tubes 30a, 32a with a consequent enhancement of the linearity of the response of the tubes to the changing tremulant control voltage applied -to the tubes.

lf desired, the output of the high frequency channel 18a and the output of the low `frequency channel 22a, as modulated by the tremulant control structure, can be mixed together and vamplified by a single power amplitier with another crossover network following.

It will be appreciated that the invention is not necessarily limited to the use of the particular `structures illustrated, but includes the use of variants and alternatives within the spirit and scope of the invention as defined by the claims.

The invention is claimed as follows:

1. In an electronic musical instrument for producing sound with tremulant elects from electronic tone signais, the combination, comprising, a source of electronic tone signals, an amplifier connected to said source, a speaker, a speaker circuit for energizing said speaker from said amplier, a magnetic core, an inductance coil on said core connected in series with said speaker circuit, two bucking coils on said core connected in magnetically bucking relation to each other, means including two vacuum tubes for energizing said respective bucking coils, and tremulant control means for supplying a cyclical control voltage to control grids of both said tubes simultaneously cyclically to vary the plate resistances of said tubes which resistances are reflected through said bucking coils and said core to said impedance coil to produce cyclic variations in the impedance of said impedance coil which produces a tremulant eect in the output of said speaker.

2. In an electronic musical instrument for producing sound with tremulant eltects from electronic tone signals, the combination, comprising, a source of electronic tone signals, an amplifier connected to said source, a speaker, a speaker circuit for energizing said speaker from said amplier, a magnetic core, an inductance coil on `Said core interconnected with said speaker circuit to control the output volume thereof, magnetizing coil means on said core, electron valve means connected to controllably energize said magnetizing coil means, and tremulant control means for supplying a cyclic control signal to said electron Valve means for cyclically varying the current through said magnetizing coil means for cyclically varying the impedance of said impedance coil which introduces a tremuylant eiect in the output of said speaker.

3. In an electronic musical instrument, means for producing sound with tremulant efIects from electronic tone signals, the combination, comprising a tone generator, an amplifier connected to said tone generator, a speaker, a speaker circuit for energizing said speaker from said amplifier, a magnetic core, an inductance coil on said core connected in output controlling relation to said speaker circuit, two bucking coils on said core connected in magnetically bucking relation to each other, means including two electron valves for energizing said respective bucking coils, and tremulant control means for supplying a cyclic control signal to said electron valves to produce a cyclical variation in the impedance of said impedance coil which produces a tremulant effect in the output of said speaker.

4. In an electronic musical instrument, means for producing sound with a tremulant effect comprising, in combination, tone generating means, an ampliiier connected to said tone generating means, crossover network means connected to said amplifier to divide the output thereof into a high frequency channel and a low frequency channel, said low frequency channel including an inductance coil on a magnetic core, a treble amplilier and a bass amplier connected to said high frequency and low frequency channels Irespectively, speakers connected to said treble and bass amplifiers, two tremulant control coils on said magnetic core electrically connected in magnetically bucking relation to each other, means including two vacuum tubes for supplying electric currents through said magnetically bucking tremulant control coils, and tremulant control means for supplying a cyclic control voltage to the grids of both said tubes cyclically to vary the current through said tremulant control coils at a tremulant frequency to produce a cyclic variation in the effective impedance of said impedance coil which produces tremulant effects in the output of said bass channel.

5. In an electronic musical instrument, means for producing sound with a tremulant effect comprising, in combination, a source of electronic tone signals, an ampliiier connected to said source, network means connected to said amplifier to divide the output thereof into a high frequency channel and a low frequency channel, a speaker connected to said high frequency channel, said low frequency channel including an inductance coil on a magnetic core, a bass amplifier connected to said low frequency channel, a speaker connected to said bass ainplifier, tremulant control coil means on said magnetic core, electron valve means for supplying electrical current through said control coil means, and tremulant control means for supplying a cyclic control signal to said electron valve means to vary the current through said control coil means at a tremulant frequency to produce a cyclic variation in the impedance of said impedance coil which produces tremulant effects in the output of said bass channel.

6. 11n sound producing means the combination of an electrical sound signal circuit having an input side and an output side, a signal control coil, a magnetic core associated with said coil to coact therewith to determine the effective inductance thereof, said control coil being connected in said circuit so that a signal passing through said circuit from the input side to the output side thereof must pass through the coil so that the signal in passing through the coil is subject to modification in accordance with the effective inductance of said coil, linx inducing coil means associated with said core, an energizing circuit for said ux inducing coil means, said energizing circuit including electronic valve means for controlling the current through said flux inducing coil means, and an oscillator connected to control said electronic valve means to eiect cyclic increases and decreases in the rate of current ow through said ilux inducing coil means at a desired tremolo frequency.

7. Means for incorporating tremolo characteristics in electronic sound signals so that tremolo characteristics are manifest in sound produced from the sound signals, comprising, in combination, an electronic signal circuit having an input side for electronic sound signals and an output side for electronic sound signals, a control coil, magnetic core means associated with said coil to coact therewith to effect determination of the inductance of the coil, said control coil being connected in said signal circuit between said input and output sides thereof so that electronic sound signals passing through said circuit must pass through said coil so that the signal in passing through the coil is subject to modification in accordance with the effective inductance of the coil, a magnetic flux inducing coil on said core, and means for energizing said flux inducing coil at a rate which is cyclically varied at a desired tremolo frequency to eifect corresponding variaftions in the effective inductance of said control coil.

8. Electrical means for producing electronic sound 4signals with tremolo effects from electronic sound sig- ,nals lacking tremolo effects, the combination of a source of electronic sound signals lacking tremolo eifects, a signal circuit having an input side connected with said source and having an output side adapted to supply signals for controlling a speaker, a control coil, a magnetic core associated with said coil to coact therewith to determine the effective inductance thereof, said coil being interconnected in said circuit so that the signals passing through said circuit from said input side to said output side thereof pass through said coil whereby the signals in passing through the coil are subject to modification in accordance with the effective inductance of the coil, two magnetic flux inducing coils associated with said core in magnetically bucking relation to each other, two energizing tubes connected to said respective flux inducing coils to energize the latter, and tremulant control means connected in controlling relation to both of said tubes to vary the output of the latter cyclically to effect cyclic variations of the current through said ilux inducing coils at a desired tremolo frequency.

9. In electrical means for producing electronic sound signals incorporating cyclic effects from electronic sound signals lacking the cyclic effects, the combination of a signal circuit having an input side for receiving unmodified sound signals and an output side for supplying modified sound signals, a control coil, a magnetic core coacting with said coil to determine the effective inductance thereof, said coil being interconnected in said circuit so that the signals passing through said circuit from said input side to said output side thereof pass through said coil whereby the signals in passing through the coil are subject to modification in accordance with the effective inductance of the coil, two magnetic flux inducing coils associated with said core in magnetically bucking relation to each other, and frequency control means connected to energize both of said ilux inducing coils at a rate which is cyclically varied at the frequency of cyclic effects desired in the sound signals.

10. In electrical means for producing electronic sound signals incorporating cyclic effects from electronic sound signals lacking the cyclic effects, the combination of electronic signal circuit means having an input side for electronic sound signals and an output side for electronic sound signals, a control coil, a magnetic core associated with said coil to coact therewith `to effect determination of the inductance of the coil, said control coil being connected in said signal circuit between said input and output sides thereof so that electronic sound signals passing through said circuit must pass through said coil so that the signals in passing through the coil are subject to modification in accordance with the effective inductance of the coil, magnetic flux inducing coil means on said core, and cyclic control means for energizing said flux inducing coil means at a rate which is cyclically varied at the frequency of the cyclic effects desired in the sound signals.

References Cited in the file of this patent UNITED STATES PATENTS 2,035,836 Ranger Mar. 31, 1936 2,466,306 Daniel Apr. 5, 1949 2,485,538 Rowe Oct. 18, 1949 2,503,352 Peters Apr. 11, 1950 2,534,342 Daniel Dec. 19, 1950 2,756,330 Krauss July 24, 1956 

